#include <fstream>
#include <bitset>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");

bitset < 2000002 > mark;

int ciur (int n){

  int prime = 1;
  for (int i = 3; i <= n; i += 2){
    if (!mark[i]){
      prime++;
      for (int j = i + i; j <= n; j += i)
        mark[j] = 1;
    }
  }
  return prime;
}


int main (){

  int n;
  fin >> n;
  fout << ciur(n);

}